Magnetic recording head asymmetry control is very important for head performance and yield. For current and future track widths, reader asymmetry control becomes a progressively more critical issue.
In the present invention we disclose a design which allows adaptive adjustment to asymmetry on individual heads by means of an additional special external or internal permanent hard magnet. This special ‘tuning’ magnet biases the shields and the sensor to achieve suitable asymmetry and/or amplification.
The biasing magnet of the present invention should not be confused with the permanent magnets used for longitudinal bias. Their purpose is the elimination of Barkhausen noise and they need to abut the sensor (specifically the free layer), which is not the case for the present invention. Furthermore, the tuning magnet of the present invention is set adaptively (its magnetization vector being adjustable) to compensate for head to head (first and second embodiments) or batch to batch (third embodiment) bias and asymmetry variations. The invention applies to all types of magnetic head including all sensor types.
A routine search of the prior art was performed with the following reference of interest being found:
Jones, Jr., in U.S. Pat. No. 5,742,998, discloses a magnetic head structure including a slider.